1. Field of the Invention
The present invention relates to an image vibration correcting device for shifting a lens within an optical axis orthogonal plane to correct image vibration due to so-called hand movements, and for example, a vibration correcting device suitable for being installed in a lens barrel, or an imaging device such as a video camera, digital still camera or the like, or an observation device such as binoculars, astronomical telescope or the like.
2. Description of the Related Art
In order to prevent image vibration due to hand movements or the like which is easily caused when shooting in a hand-held condition, various devices have been proposed for realizing vibration correction by detecting vibration information of a camera or binoculars and optically canceling the vibration based on the detection results.
For example, in U.S. Pat. No. 6,112,028 (Japanese Laid-Open No. 305277 of 1999), a so-called shift-method vibration correcting device is proposed in which a vibration correcting lens group among a plurality of lens groups is shifted in an optical axis orthogonal plane to correct vibration.
In a vibration correcting device relating to this proposition, three pins are radially press-fitted to a shift member holding the vibration correcting lens group, and engaged into slots formed at three portions in the circumferential direction of a fixed member which is the device main body while leaving a space, and guided so that the vibration correcting lens group can be shifted within the optical axis orthogonal plane.
In this vibration correcting device, the pins are pressed toward one side in the optical axis direction in the slots by using magnetic attraction acting between a magnet and a ferromagnet, whereby looseness inside this guide portion and tilt of the vibration correcting lens group due to the looseness are prevented. Thereby, optical performance is maintained and operation noise caused by looseness at the guide portion when driving is reduced.
In the vibration correcting device disclosed in U.S. Pat. No. 5,602,675 (Japanese Laid-Open No. 289465 of 1994), in a flexible substrate connecting a circuit board provided in the fixed member and a coil provided at the shift member, by contrivance in the shape and arrangement of an extended portion to reduce loads in the optical axis direction and shift two directions, harmful influences to the drive of the shift member are prevented.
Furthermore, in the vibration correcting device disclosed in U.S. Pat. No. 6,064,827 (Japanese Laid-Open No. 319465 of 1998), the objects to eliminate looseness between the fixed member and the shift member in the optical axis direction and reduce drive resistance of the shift member against the fixed member are achieved by disposing a rolling ball between the fixed member and the shift member and pressing the shift member is prevented by a spring pressing force against the fixed member via the ball.
In this vibration correcting device, a structure has been employed in which the shift member is guided in the shift direction by the ball rolling, and the shift member is prevented from rotating about the optical axis by a spring.
Recently, in imaging devices and observation devices to which lens barrels are mounted, in order to improve portability and containing performance, a downsized design or a design with fewer projections has been demanded, and in accordance with this tendency, downsizing is also required for lens barrels and vibration correcting devices.
However, if a lens barrel is downsized, a space for locating a vibration correcting device main body or a flexible substrate connecting the fixed member and shift member is remarkably limited, and as a result, it becomes difficult to sufficiently lower the rigidity of the flexible substrate. Therefore, in U.S. Pat. No. 5,602,675, it is difficult to lower an elastic force in the optical axis direction to be generated on the flexible substrate to a permissible level by only contrivance in the shape and arrangement of the flexible substrate.
Therefore, in U.S. Pat. No. 6,112,028, even if the shift member is pressed in the optical axis direction by a proper force while using a magnetic attractive force, due to unevenness in the elastic force in the optical axis direction of the flexible substrate, the pins of the shift member are excessively pressed into the slots and resistance greatly increases, or to the contrary, pressing by means of the magnetic attractive force is canceled, and this harmfully influences the drive of the shift member.
On the other hand, in the field of image pickup devices such as a CCD or the like for converting a subject image formed on a focus plane by a shooting optical system into an electric signal, in accordance with advanced semiconductor fine processing techniques, manufacturing of an imaging device with smaller pixel pitches has become possible.
Accordingly, two mainstreams have been developed, that is, further downsizing of optical systems by forming an equivalent number of pixels to that of a conventional art within a smaller area, and a further increase in resolution of optical systems accompanied with an increase in the number of pixels within the same pixel area or due to pixel area expansion.
In the former case, since the shift amount of the vibration correcting lens group for correcting the same amount of vibration is roughly in proportion to the imaging area, more minute movement is required, and the location space for the flexible substrate also becomes smaller.
In the latter case, resolution may deteriorate unless correction of minute vibration is possible, so that minute movement of the shift member must be made possible by lowering the frictional force generated at the guide portion.
In all cases, higher accuracy relative to the tilt of the vibration correcting lens group is required.
Furthermore, in the vibration correcting device disclosed in U.S. Pat. No. 6,064,827, the ball is held by a holding member so as not to change in position with respect to the fixed member, the ball and shift member are guided by means of rolling. However, since the ball rolls at the position at which the ball is held by the holding member, sliding frictional forces are generated between the ball and fixed member and between the ball and shift member.
Therefore, the pressing force of a spring for eliminating looseness is limited to be at a minimum level required for holding the ball, so that the shift member separates from the ball due to slight acceleration in the optical axis direction resulting from an inertial force exceeding this pressing force applied to the shift member, and the deterioration in optical performance due to tilt of the vibration correcting lens group and noise such as a ball striking sound becomes a problem.
For example, when a shift member with a 4 g weight is pressed by a 4 gf force, application of only 1 G or more of acceleration causes the shift member to separate from the ball.
The prevention of rotation of the shift member about the optical axis by means of a spring relies on the pulling force of the spring, so that the rotation cannot be completely stopped, and the force can only suppress the rotation.
Particularly, in the construction of the means for detecting the position of the shift member which is disclosed in the above-mentioned U.S. Pat. No. 6,064,827, an output value of the position detecting means changes due to the rotation about the optical axis. Therefore, depending on the positional relationship between the force generating position at which the drive means generates a shifting drive force and the center of gravity of the shift member, or the connected position and shape of the flexible substrate connected to a coil on the shift member, the shift member rotates about the optical axis in accordance with the shifting drive, and the drive of the vibration correcting lens group to a correct position for vibration correction becomes impossible.